Are there deficits in anticipatory postural adjustments in Parkinson's disease?

We studied anticipatory postural adjustments in patients with Parkinson's disease who dropped a load from extended arms while standing. Anticipatory postural adjustments were seen when load dropping was induced by a fast, bilateral shoulder abduction but not when it was induced by pressing a trigger with the right thumb. We conclude that anticipatory postural adjustments in patients with Parkinson's disease can change with the magnitude of an action which is used to trigger a predictable postural perturbation. Thus, the described deficits in anticipatory postural adjustments in patients with Parkinson's disease are likely to be of quantitative rather than qualitative nature.